Species diversity and trophic structure

Question 1

Diversity

Answer 1

number of species within a community

Question 2

Benefits of biodiversity

Answer 2

• Stability (better able to
  withstand disturbances
  and invasive species)
• Higher productivity

Question 3

Trophic structure:

Answer 3

The structure and dynamics of a community
are shaped by the feeding relationships between organisms

Question 4

Energy in the form of food flows through…

Answer 4

food chains
* From Primary Producers
* To Primary Consumers
* To Primary Carnivores
* To Secondary Carnivores

• … and Decomposers
• … and Bacteria, fungi, protists

Question 5

Food chains

Answer 5

• Are useful for simplifying/
  modelling natural situations
• In the real world there are
  multiple links across trophic levels

Question 6

Food webs

Answer 6

the common model of trophic structure
Highly complex - animal diets vary in space and time
‘Rewiring’
Very few, if any, natural systems have been fully
described

Question 7

How to study food webs - identify what animals eat

Answer 7

• Direct observation
• Regurgitates
• Pellets
• Gut contents
  (kill or stomach pump)
• Stable Isotopes - N15 has
  higher retention in animal
  tissues than N14. N15
  accumulates at increasing
  trophic levels

Question 8

Studying food webs - mathematical modelling

Answer 8

• Very important in the study of food
  webs
• Enables us to examine a numbers of
  ecological scenarios (e.g. what happens
  if different species are removed or
  added to a community)
• Often requires advanced maths and
  high levels of computing power to
  model whole communities
  Diversity-stability paradox/debate – empirical evidence says more diverse, more
  stable

Question 9

Energetic hypothesis

Answer 9

Only around 10% of the energy
stored in organic matter of each
trophic level…
… is converted into organic matter
at the next trophic level
Prediction: food chains should be longer in habitats of higher primary productivity
Amount of energy at the bottom of the food chain is greater
More energy is available to be transferred to higher
trophic levels

Question 10

Dynamic stability hypothesis

Answer 10

Long food chains are less
stable than short food chains
* Population fluctuations at
lower trophic levels are magnified at higher trophic levels
Prediction: food chains should be
shorter in unpredictable environments
Environmental fluctuations
reduce population sizes at low trophic levels
As a result high trophic levels become extinct
Most of the data collected so far support the energetic hypothesis

Question 11

Other factors limiting length of food chains

Answer 11

SIZE MATTERS
Animals at higher trophic levels are usually larger than animals at lower trophic levels
* The size of an animal and its feeding mechanism limit the size of food it consumes
* Generally large carnivores cannot survive by feeding on small animals
* High energetic cost of finding/catching/consuming ‘small’ organisms
* Upper size limit

Question 12

Exceptions to size matters

Answer 12

Some animals can feed on very large numbers of smaller animals
Baleen whales, Basking sharks et al.